Engineers investigate another malfunction on SpaceX’s Falcon 9 rocket

SpaceX is investigating a problem with the Falcon 9 rocket's upper stage that caused it to reenter the atmosphere and fall into the sea outside of its intended disposal area after a Saturday launch with a two-man crew heading to the International Space Station.

The upper stage malfunction apparently occurred after the Falcon 9 successfully deployed SpaceX's Crew Dragon spacecraft carrying NASA astronaut Nick Hague and Russian cosmonaut Aleksandr Gorbunov on SpaceX's Crew-9 mission. Hague and Gorbunov safely arrived at the space station Sunday to begin a five-month stay at the orbiting research complex.

The Falcon 9's second stage Merlin vacuum engine fired for more than six minutes to place the Crew Dragon spacecraft into orbit after liftoff from Cape Canaveral Space Force Station, Florida. The engine was supposed to reignite later to steer the upper stage on a trajectory back into Earth's atmosphere for disposal over the South Pacific Ocean, ensuring the rocket doesn't remain in orbit as a piece of space junk.

"After today’s successful launch of Crew-9, Falcon 9’s second stage was disposed in the ocean as planned, but experienced an off-nominal deorbit burn," SpaceX posted on X late Saturday night. "As a result, the second stage safely landed in the ocean, but outside of the targeted area. We will resume launching after we better understand root cause."

Safety warnings issued to mariners and pilots before the launch indicated the Falcon 9's upper stage was supposed to fall somewhere in a narrow band stretching from southwest to northeast in the South Pacific east of New Zealand. Most of the rocket was expected to burn up during reentry, but SpaceX targets a remote part of the ocean for disposal because some debris was likely to survive and reach the sea.

SpaceX didn't release any more details on the upper stage malfunction. Jonathan McDowell, an astrophysicist and expert on spaceflight activity, wrote on X that the most likely failure mode that would still result in a reentry is a "slight underburn" of the Merlin vacuum engine. This would result in the rocket going off course and reentering somewhere over the Pacific Ocean farther downrange, northeast of the projected disposal area.

Third time in three months

This is the third time SpaceX has grounded the Falcon 9 rocket in less than three months, ending a remarkable run of flawless launches.

SpaceX's upper stage failed during the July 11 launch of a batch of 20 Starlink Internet satellites, stranding the payloads in a lower-than-planned orbit that caused them to reenter the atmosphere and burn up. This was the first mission failure for a Falcon 9 rocket in 335 missions since 2016, a record unmatched in the history of space launch vehicles.

Engineers traced the problem to a crack in a "sense line" for a pressure sensor attached to the vehicle’s liquid oxygen system, resulting in a liquid oxygen leak that prevented the rocket from completing the second burn of its upper stage engine. While Saturday's upper stage issue is still under investigation, it also arose on the second burn of the Merlin vacuum engine.

The sense line is redundant, so SpaceX removed the component and successfully resumed launching the Falcon 9 rocket 15 days later.

Then, on August 28, a reusable Falcon 9 booster tipped over moments after landing on a drone ship in the Atlantic Ocean. This launch with another batch of Starlink satellites was otherwise a success, but this marked the first time SpaceX lost a rocket after landing 267 boosters in a row.

After both of these flights, the Federal Aviation Administration required SpaceX to conduct an investigation into the failures. The FAA is the regulatory agency that licenses commercial launch vehicles, and its responsibility includes ensuring launch and reentry operations do not endanger the public.

The FAA allowed SpaceX to resume launches after these two incidents after determining the failures did not have an impact on public safety. After the July 11 and August 28 incidents, the FAA issued a "public safety determination" that allowed SpaceX to return to flight with the Falcon 9 rocket after 15 days and three days, respectively.

SpaceX said it was putting Falcon 9 flights on hold after the problem with the Falcon 9 upper stage Saturday. As of early Monday, the FAA had not responded to questions from Ars on whether the agency will mandate an investigation.

The upper stage malfunction over the weekend is unlikely to ground the Falcon 9 rocket for long, but SpaceX has already postponed the next Falcon 9 launch, which was scheduled to lift off Sunday night from Vandenberg Space Force Base in California with a group of Internet satellites for OneWeb. A Falcon 9 launch from Cape Canaveral with Starlink satellites Wednesday has also been delayed.

The Falcon 9 rocket is a workhorse in the launch industry, flying an average of about one mission every three days. While history suggests SpaceX will resume flying the Falcon 9 rather quickly, important interplanetary science missions are hanging in the balance.

A Falcon 9 rocket is scheduled to launch October 7 with the European Space Agency's Hera spacecraft to visit the binary asteroids Didymos and Dimorphos and investigate the system after the impact of NASA's DART spacecraft in 2022. DART tested an asteroid deflection technique that could move an object off a collision course with Earth.

Three days later, on October 10, SpaceX is supposed to launch NASA's $5.2 billion Europa Clipper mission on a Falcon Heavy rocket to begin a six-year journey to Jupiter, where it will explore one of the giant planet's icy moons. The Falcon Heavy uses essentially the same upper stage design as the Falcon 9.

Both of these missions will require two burns of the upper stage's Merlin vacuum engine to send the Hera and Europa Clipper spacecraft out into the Solar System. They also have limited launch windows to depart Earth and still reach their destinations. Hera's launch period runs from October 7 through October 27, and Europa Clipper's window extends from October 10 through November 6.